输入验证码:<%=text_field(:proof, :text, :maxlength=>4) %>
<img id="img" src="/chen/util/proof_image">
<a href="#" onclick="changeImage();return false;">换一个验证码</a><br/>

<script>
function changeImage(){
  $("img").src = "/chen/util/proof_image?tmp=" +new Date().getTime(); // Math.random();
}

</script>
